The invention relates generally to fluid flow control dampers and more particularly to a low pressure fluid operated fluid flow control damper assembly particularly useful in HVAC systems.
Fluid flow control dampers are used in a wide variety of applications, including (heating, ventilation and air conditioning) HVAC systems. In HVAC systems, dampers are used to control the supply of conditioned air to various rooms or zones within a building. One such damper device is a mechanical damper assembly including a short piece of duct in which a damper vane is pivotally mounted by a shaft. The damper vane is rotatable between open and closed positions by a motor that is mounted outside the duct and connected to the vane shaft.
The aforesaid type of mechanical damper assembly is somewhat difficult to install in an existing duct. Installation requires the duct piece of the damper assembly to be spliced into an existing duct. This involves cutting a length from the existing duct and usually dismantling the existing duct to enable such cutting and/or assembly of the duct piece between adjacent sections of the existing duct. This dismantling, cutting and reassembly of the duct work is time consuming and expensive.
Dampers also have been employed at room registers to control the flow of air into a room. These dampers typically include a pivotally mounted damper vane on the duct side of the register and an actuator lever which protrudes on the room side of the register for enabling manual adjustment of the damper vane. The dampers are wall or ceiling mounted over a duct opening or slip fitted in a duct opening provided in the floor.
Also known are pneumatically actuated damper assemblies. Reference may be had, for example, to U.S. Pat. No. 5,458,148 which discloses a self-contained unit comprising a support base for external mounting to a side of a duct and a damper vane mounted to the support base for movement between open and closed positions. The damper vane is located inwardly of the inner side of the support base for positioning interiorly of the duct when the support base is mounted to the duct. An actuator is mounted to the support base at the exterior side thereof and is operatively connected to the damper vane by a linkage for moving the damper between the open and closed positions. The support base functions to close an access opening in the side wall of the duct of sufficient size to permit insertion of the damper vane therethrough.
The present invention provides a novel fluid flow control damper assembly that overcomes drawbacks associated with and/or improves upon prior art damper assemblies. Several embodiments of a damper assembly according to the present invention are self-contained units that are compact and relatively easy to install in existing ducts, including in situations where the outside surface of the duct is inaccessible.
A damper assembly according to one aspect of the present invention includes a damper vane and a pneumatic piston-cylinder actuator connected to the damper vane for moving the damper vane between an open position and a closed position. The piston-cylinder actuator includes a piston and a cylinder that have cooperating nonelastomeric sliding sealing surfaces which provide essentially friction-free axial movement of the piston relative to the cylinder. The surfaces at the sliding interface between the piston and the cylinder preferably are smooth and function to provide a substantially air tight seal, thereby eliminating the need for elastomeric seals that normally would introduce additional friction into the actuator.
The piston and/or the cylinder are formed of a material selected from the group including metal, powdered metal, resin, glass, and polymer. The piston and/or the cylinder also may have a friction-reducing coating on the sealing surface thereof. Preferably, the piston-cylinder actuator has a powder-metal piston and a glass cylinder.
According to another aspect of the invention, the damper assembly includes a base, to which the damper vane and the piston-cylinder actuator are mounted, preferably on the same side of the base as the piston-cylinder actuator. The actuator may be controllably connected to a pneumatic control system through a fitting at one end of the cylinder, and the fitting may have a threaded portion for mounting the actuator with respect to the base. The base may be configured for mounting to the exterior of a duct, in which case the piston-cylinder actuator may be mounted to the base with a nipple portion of the actuator fitting is disposed at an exterior side of the base for connection to the pneumatic control system. As a result, the piston actuator presents a minimal profile outside the duct, which is advantageous in shallow clearance situations, as well as providing an improved appearance.
The damper vane and the piston-cylinder actuator may be interconnected by a drive rod. The drive rod may be mounted to transfer substantially only axial forces from the actuator to the damper vane, for example, by using ball joints to connect the ends of the drive rod to the damper vane and the actuator piston. This arrangement prevents lateral or twisting forces from acting on the drive rod, which otherwise may cause the piston to bind in the cylinder. In addition, the actuator does not have to be precisely aligned with the damper vane, thereby facilitating manufacturing and installation.
The piston-cylinder actuator also may have a cylindrical cap that fits over an end of the cylinder to retain the piston in the cylinder. The cap has an oversized opening for passage of the drive rod therethrough. Particularly if the cylinder is made of glass, a substantially cylindrical protective boot may be used to substantially cover the outer circumferential surface of the cylinder. The boot preferably is made of an elastomer, such as rubber, to protect the cylinder, particularly prior to and during installation.
The damper vane also may include a plurality of damper vanes that cooperate to close a cross-section of a duct when the damper vanes are in closed positions, and a plurality of piston actuators. Each piston actuator is operatively connected to one of the damper vanes for opening and closing the damper vanes. The plurality of damper vanes may include a first damper vane that has an aperture, and a second damper vane that closes the aperture when both the first damper vane and the second damper vane are in their respective closed positions. The damper vanes lie in substantially parallel planes when both the damper vanes are in their open positions to present a minimal profile to the airflow. The plurality of damper vanes are used to supply different volumes of air through the damper assembly to mix fresh air with return air in varying proportions, to provide a varied amount of conditioned air according to varied requirements and/or to supply a constant but smaller amount of airflow until a greater or full amount of air supply is needed.
The damper assembly may include a spring connected to the damper vane for biasing the damper vane to a predetermined position. This feature is particularly advantageous in the event of a power failure, to automatically open or close the damper vane under the action of the spring.
According to another aspect of the invention, a damper assembly may have a frame, a damper vane mounted to the frame for pivotal movement between open and closed positions, and an actuator for moving the damper vane between the open and closed positions. The frame has a cross-sectional shape that approximates or generally corresponds to a cross-sectional shape of a duct into which the damper assembly may be installed. The frame preferably has a gasket or elastomeric member disposed on the exterior thereof or positioned about at least a portion of its outer periphery to sealingly engage the frame with a duct wall. The actuator is located within the confines of a projection of the frame in an axial direction. Accordingly, the damper assembly may be inserted into an open end of a duct with the actuator disposed within the duct.
According to a further aspect of the invention, there is provided a method of installing a damper assembly, the method including the steps of removing a register from an outlet of a duct, inserting the damper assembly into a duct adjacent the outlet, and replacing the register. Thus, the simple method provided by the present invention may be used to retrofit a building where access to the ductwork is otherwise unavailable.
According to another aspect of the present invention, a damper assembly may include at least two duct wall-engaging members movable towards each other against a biasing force. The duct wall-engaging members preferably apply substantially equal forces against opposing walls of the duct to center and align the damper assembly in the duct. The duct wall-engaging members may apply unequal force against the duct wall to position the damper assembly off-center as well. The duct wall-engaging members may be formed by a leaf spring extending from lateral sides of the base, and may have integral handle portions for easily grasping the damper assembly for insertion into a duct. Installation in a duct may be affected by retracting the duct wall-engaging members against the biasing force, inserting the damper assembly into the duct, and releasing the duct wall-engaging members so that the biasing force presses the duct-wall engaging members against the duct walls to hold, align and preferably center the damper assembly in a fixed location within the duct. A damper assembly having such wall-engaging members is particularly advantageous when the external surface of the duct is inaccessible, permitting the damper assembly to be installed from an end of the duct, perhaps with just one hand. Automatic self-centering is a particular advantage in a blind installation where the installer cannot easily see into the duct. By automatically centering the damper assembly, the present invention also minimizes the chance that rigid portions of the damper vane would scrape against the duct wall as the damper vane moves between its open and closed positions. The damper assembly is thus more likely to operate quietly.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail certain illustrative embodiments of the invention, these embodiments being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.